EXAM REVIEW FALL 2013.docx

30
Pages

260
Views

Unlock Document

School

York University

Department

Psychology

Course

PSYC 1010

Professor

Agnieszka Kopinska

Semester

Winter

Description

York University
Fall Term 2013 Examination:
NATS 1780
Weather & Climate
Content:
o Geoscientific Thinking/Learning
o Clouds and Fog
o Condensation
o H2O
o Stability and Structure
o Cloud Formation and Precipitation
o Composition
o Radiation
o Aerosols
o Temperature
Geoscientific Thinking/ Learning
­ Time
­ Space
­ Practice
­ Systems­orientation
Time
Weather vs. Climate
Weather:
The condition of the atmosphere at a particular time and place
o Temperature
o Pressure
o Humidity
o Clouds
o Precipitation
o Visibility
o Wind
o ….
Climate:
The ‘average weather’
o Accumulation of daily and seasonal weather events over a long period of
time
o Extreme events
o Heat waves
o Cold spells
o The frequency of evens distinguishes climates as much as the averages Space
­ “Geoscientists use spatial thinking extensively whenever they acquire, represent,
manipulate, or reason about objects, processes, or phenomena in space.”
Practice
• Professional vision
o The ability to see features that are important to professional practice
• “… field experiences provide practice in transforming the raw material of nature
into the words, signs, and symbols that geoscientists use to capture and
communicate their observations.”
Systems­orientation
What is a scientific model?
• A representation of empirical objects, phenomena, and physical processes that is
logical and objective
• Models are simplified reflections of reality
• Building and disputing models is fundamental to science
Summary:
­ Time, space, practice and systems­orientation are key to geoscience
thinking/learning
­ Geoscience thinking/learning skills are of use beyond geoscience courses…
BUT… geoscience needs thinking/learning skills developed outside of the
geosciences.
Clouds & Fog
Classification of Clouds
• Luke Howard (1803)
• Introduced a classification system
o Based on observations from the ground
• Four basic cloud forms
o Stratus (Latin for layer)
o Cumulus (Latin for heap)
o Cirrus (Latin for curl of hair)
o Nimbus (Latin for violent rain)
• Abercromby and Hildebrandsson
o Modified Howard’s system
o Resulting classification system still used today
• 10 basic cloud forms
o 4 primary cloud groups
 High Clouds
 Middle Clouds
 Low Clouds  Vertical Clouds
1. High Clouds
• Altitude of 6­13km (in midlatitudes)
o At this altitude the air is cold and dry
 Favors formation of ice clouds (almost exclusively)
 These clouds appear thin
• Three forms
o Cirrus (Ci)
 Thin wispy clouds blown by high winds
 Mares tails
 Most common of the cirrus group
 Mostly comprised of ice crystals
o Cirrocumulus (Cc)
 Has a rippled appearance
 Looks like fish scales
o Cirrostratus (Cs)
 Thin, sheet­like high clouds
 Often cover the entire sky
 Can see the Sun and/or Moon through them
 Light is refracted by ice crystals
 Results in halos
 Often form in advance of a storm
 Used to predict an approaching storm
2. Middle Clouds
• Altitude of 2­7km (in midlatitudes)
• Composition
o Ice water droplets (primary)
o Ice crystals (secondary)
o Altocumulus (Ac)
 Grey fluffy masses
 Can see individual puffy mass
 At arms length are about the size of your thumb
o Altostratus (As)
 Extensive gray mass
 Often covers the entire sky
3. Low Clouds
• Altitude under 2 km
• Almost always composed of liquid water droplets
o In cold weather, may contain ice or snow
• Three forms
o Stratus (St)  A uniform gray cloud
 Often covers the entire sky
 Resembles a fog, that doesn’t quite reach the ground
 Has a low base
 No rain falls from stratus (normal)
 Light mist or drizzle (occasional)
o Stratocumulus (Sc)
 A low, lumpy cloud layer
 Lumps appear larger than from Ac)
 Has a lower cloud base than Ac
 At arms length, is about the size of ones fist
 Rain or snow rarely fall from Sc
o Nimbostratus (Ns)
 A dark, ‘wet­looking’ cloud layer
 Associated with raining­all­day days
 Associated with light to moderate precipitation
 Rain or snow
 Often low visibility beneath the cloud deck
 Blocks light
 Low, irregular cloud base
4. Vertical Clouds
• Clouds having vertical structure
• Flat cloud bases and puffy, domed tops
• 2 forms
o Cumulus (Cu)
 ‘Fair­weather’ cumulus
 Look like floating pieces of cotton
 Clouds are separate and distinct
 Show only slight vertical growth
 Often form on warm, sunny days
 If liquid water falls, its only showery
 Cumulus congestus
 Towering cumulus
o Cumulonimbus (Cb)
 As cumulus congestus continues to grow it becomes Cb
 Associated with thunderstorms, thunder and/or lightning
 Violent updrafts
 Vertically extensive
 Base can be as low as 300m
 Can top out in the tropopause at over 11km
 Low in the cloud, liquid water present
 High in the cloud, ice can be formed  High winds at upper levels can shape the cloud to form an
anvil
 Can produce all types of precipitation
What are clouds?
­ Droplets of liquid water and/or ice crystals
­ Observing clouds from above (eg. Aircraft)
o Light is reflected off the cloud (cf. albedo)
 The cloud appears bright
­ Observing clouds from below (eg. Ground)
o Light has passed through the cloud
 …and has been attenuated by the cloud
 The denser and larger the droplets, the more light is attenuated, and
the darker the cloud appears.
Scattering of Light
• Redirection process
• Scatterers (particles/gases) determine:
o Quantity
o Geometry
o Wavelength dependence
Classification of Fogs
• Process­based classification
o Radiation Fog
 Processed by radiative cooling of Earth’s surface
 As Earth cools after sunset, air above it cools
 As air temperature decreases, RH increases until saturation results
in condensation
 As temperature continues to decrease, condensation results in
droplet growth
o Advection Fog
 Warm, moist air (water) moves over colder surface (land)
 Air cools, saturation occurs, and condensation
o Upslope Fog
 When air is forced to rise due to topography
• Eg. The presence of a hill or mountain
 As the air mass rises, it expands and cools
• If it cools to saturation, condensation may begin (if CCN
present)
o Evaporation Fog
 When mixing of two, unsaturated air masses results in the
formation of a saturated air mass  In cold weather bodies of water are often warmer than the
surrounding air
 A layer of air above the water can be moist
 When this layer of air mixes with the cold air above it, the mixture
can become saturated
 Condensation occurs, fog results
Condensation
­ Latent Heat
o Hidden energy
o Energy that is used to break molecular structure, not bonds
o When changing phases, temperature remains constant
o Heat will be released or required
­ Stored energy
o Energy from the Sun can be stored
o Solar energy is absorbed by liquid water
o Results in some of the liquid water becoming water vapor
o Stored energy can be released, elsewhere in the atmosphere
o When the water vapor condenses
­ In a system containing two or more phases
o There is a constant exchange of molecules between the phases
o Equilibrium is established when the exchange between the phases is
equivalent
­ Condensation
o The rate of water vapor being deposited to the surface is faster than the
rate of water molecules leaving the surface. Energy is released, and the
surroundings are warmed.
­ Evaporation
o The rate of water molecules leaving the surface is faster than the rate of
water molecules being deposited to the surface. Energy is required, and the
surroundings are cooled.
­ Vapor Pressure
o Molecular collisions exert a force (force can be exerted on a wall, person,
etc.)
o Therefore, pressure = force / area
o Therefore, pressure is dependent upon the number of molecules colliding
with an area of a surface
­ Saturation Vapor Pressure
o The pressure of the vapor of a substance in equilibrium with its condensed
phase (solid or liquid) is called the saturated vapor pressure
o This is the maximum amount (with super saturation) of a molecule that
can be found in the vapor phase at a particular temperature and pressure
­ Saturation
o Equilibrium between the liquid and vapor phase. For every molecule that
evaporates another must condense. This is dependent upon the temperature
and pressure ­ Unsaturated Air
o Air that is holding less water than it could possibly hold. Therefore: non­
equilibrium evaporation is occurring.
o Note: objects will dry in unsaturated air, but not in saturated air.
­ Humidity
o Refers to the amount of water vapor in the air
 Absolute humidity, the weight of water vapor within a specific
volume (g/m^3)
o Specific humidity
 The weight of water vapor relation to the total mass of the air
parcel (g/kg)
­ Relative humidity
o The ratio of the amount of water vapor actually in the air compared to the
maximum amount of water vapor required for saturation at that particular
temperature and pressure.
o RH = (H2O (g) content) / (H2O (g) capacity) x 100%
o Eg. An air parcel with RH = 25%, contains only 25% of the total water
that the air parcel could hold.
o Can alter RH by
 Changing the amount of water vapor in an air parcel
 Changing the capacity of the air parcel to hold water (change the
temperature)
Why Use Relative Humidity?
• Importance WRT condensation/evaporation
• Evaporation
o The greater the difference between the amount of water vapour in the air
and the amount that it could hold (lower the RH)
 The higher the rate or evaporation
o On a very humid day (high RH)…
 Feel hotter, sweat on our skin does not evaporate as quickly, less
cooling effect
 Wet clothes don’t dry as quickly, etc.
Evaporation & Relative Humidity
­ The lower the relative humidity, the faster the rate of evaporation – better cooling
­ The higher the relative humidity, the slower the rate of evaporation – poor cooling
Relative Humidity and Condensation
­ Condensation
o The higher the RH
 The closer the air is to saturation
 Less cooling will have to take place in order for the air to become
saturated
o Very important to cloud formation Dew Point
­ The temperature at which an air mass becomes saturated
o RH = 100%
­ Basis for comparison
o Compare the ambient temperature with Td
 Means for assessing how close to 100% RH an air mass is
­ The dew point is a physical property that serves to characterize an air mass
­ Suppose that…
o Day: T = 29 C and RH = 75%
o Night: T = 23 C and RH = 100%
o The air mass is saturated
o Further cooling
o Condensation starts
o Liquid water (dew) is formed
­ Can use the dew point to calculate RH
­ RH = (SVP @ Td) / (SVP @ T) x 100
­ Where SVP = saturated vapor pressure
­ Can use a wet­bulb thermometer to measure the dew point
­ Frost Point
o If the freezing point of water is reached before saturation… Then the
saturation point is the frost point, not the dew point
o When the air becomes saturated, water vapor is deposited to surfaces as a
solid (frost, hoarfrost, white frost)
­ Measuring Relative Humidity
o Wet­bulb temperature
 The lowest temperature that can be reached by evaporating water
into air
 Simulates the cooling effect of water on the skin
 The bulb of a thermometer is coated with a wick (a piece of cloth)
and wetted (with water)
 Evaporation of the water results in cooling
 RH determined by a chart
o Psychrometer – Wet and Dry Bulb
 Contains a wet­bulb (wetted thermometer) and a dry­bulb
thermometer
 Using the difference between these two temperatures
• … and the dry bulb temperature
• … the RH can be calculated
 eg. Suppose
• A dry bulb temperature reads 27.5C • A wet bulb 24C
• Depression is 3.5
• RH is 75% (via chart)
­ Measuring Dew Point Temperature
o Psychrometer – Wet and Dry Bulb
 Same as to measure RH
 Obtain the wet and dry­bulb temperatures
 Calculate the wet­bulb depression
 Difference between wet and dry
 Look up the dew­point temperature on a chart
­ Humidex – Heat index
o Accounts for humidity effect on temperature
 The higher the humidity …
 …. The less efficiently we can cool ourselves
 therefore hotter it ‘feels’
 Apparent temperature
­ Condensation
o At 100% RH, clouds or fog are not always seen forming
o A surface is required for the water vapor to condense onto
o These surfaces are referred to as aerosols
o Serve as nuclei for the formation of clouds OR cloud condensation nuclei
(CCN)
­ Super­saturation
o If no surface is available… the air mass becomes supersaturated
o ▯RH > 100%
­ Condensation Nuclei
o Air contains aerosols
 Small particles suspended in air
• Solid or liquid or a combination
• Range in size from 0.01 um to 100’s of um
o Similar to a liquid which also requires a surface before freezing
o Can supercool (T<0C) in the absence of freezing nuclei
 Eg. A 1 um droplet
 … Can stay unfrozen to ­40C
­ Diurnal diabetic heating ▯ temp. Variation
o Diurnal diabetic heating ▯temperature variation
 Radiation process flows
• Atmospheric albedo ignored
 Atmospheric absorption ignored  Ignore phase changes in H2O
 ‘No loss” Earths surface (­closed system)
• Albedo of Earths surface ignored
• Atmosphere absorbs all re­emitted IR
 No loss to space
 Ignore re­emitted IR from the atmosphere
 ‘Clear sky Summertime’
 No active storm systems
• H pressure system
H2O in Earths Atmosphere
­ Hydrogen Bonding
o A weak interaction between the Hydrogen in one molecule with the
Oxygen in another molecule
­ Characteristics of H2O
o Is a liquid
o When heavier­mass molecules are gases
 Eg. H2o = 18g/mole, O2 = 32 g/mole
o Over a very large temperature range
o Has a large heat capacity
o Has the ability to store large amounts of heat
o The density of the solid is less than the liquid, therefore lie floats
­ H2O in the atmosphere
o The most­variable constituent of the atmosphere
o Found in all three phases in the atmosphere
 Solid, liquid, and vapor
o An infrared­active gas
 An important greenhouse gas
o Large latent heat capacity
 Releases or extracts large amounts of heat upon changing phases
• Regarding as a ‘hidden heat’
­ The Hydrological Cycle
o H2o is cycled on Earth
o Solar energy evaporates water
o Air laden with water vapor can rise and condense
o Rain can occur
o Followed by ground water run off
 Note: this is the process by which ALL fresh water is produced
­ Phase Relations for H2O o Phase
 Any sample of matter with definite composition and uniform
properties
 Distinguishable from other phases in which it is in contact
o Attention focuses on all three phases of H2o
 Liquid, vapor and solid
• … and transitions between them
• … that do not involve chemical reactions
­ Energetics of Phase Changes
o Energy released
 Exothermic phase change
• Condensation
• Freezing
• Deposition
 Energy absorbed
• Endothermic phase change
o Evaporation
o Melting
o Sublimation
Stability & Structure ­ In the troposphere temperature decreases with height
­ Atmospheric Stability overview
o Density (parcel) Density (environment)
 Parcel sinks
 Pressure increase ▯compression/warming
o Density (parcel) = Density (environment)
 Parcel stationary
Adiabatic Processes: Dry
­ No interchange of heat, between the parcel and its environment
o During expansion/cooling or compression/warming
­ Dry adiabatic lapse rate (DALR)
o Air in the parcel is unsaturated, RH <100%
­ Γ dry = 10C per km
Adiabatic Processes: Moist/Saturated
­ No interchange of heat, between the parcel and its environment, during
expansion/cooling or compression/warming
­ Moist adiabatic lapse rate (MALR)
o Γ Moist = 6.5 C per km
­ Less than the dry adiabatic lapse rate
o Γ moist Density (environment)
 Parcel sinks, air stable
­ Temperature (parcel) > Temperature (environment)
o Density Parcel 1 year
­ Stratosphere: Ozone Photolysis
o Stratospheric heat source
o Incident UV radiation
 Absorbed by ozone
 Ozone breaks apart
 ▯Molecules have more energy
 Temperature increases
­ Stratospheric Inputs
o Little weather occurs in this region
o Tropospheric inputs
 Direct, rapid
• Volcanoes, very large storms, etc.
 Diffusive, slow input
• Gases
o Response to inputs
 Vertical mixing takes a very long time
• Based on diffusion
 Horizontal mixing is very fast
• Winds speeds are very high
­ Troposphere­Stratosphere Interactions